"We have made considerable progress," said Jack Szostak, an artificial life investigator at the Howard Hughes Medical Institute in Chevy Chase, Md. "Any prediction like this is just a guess, but I'm hoping we'll have a synthetic cell in under 10 years."

Such a cell would be "unrelated to any existing life form on Earth," Szostak said.

Other experts, however, said it might take decades or centuries before scientists would be able to "create life from scratch," as the quest is colloquially known.

Meanwhile, researchers are laboriously modifying and assembling existing biological molecules to construct synthetic cells with some -- but far from all -- of the attributes of living creatures.

So far, what they're doing is more like copying nature's clever tricks than creating new life forms in the laboratory, with all the tremendous philosophical, social and religious issues that such a stunning feat would imply.

"Creating artificial life is very different from reproducing what existed already in nature," said Eckhard Wimmer, a microbiologist at Stony Brook University on Long Island, NY. "That (artificial life) may be possible in the future, but this future may be hundreds of years away."

According to Szostak, a living cell has two essential needs: First, a set of genes that contain instructions for it to eat, grow, divide and reproduce, and second, a surrounding membrane or wall that separates its contents from the outside world but allows nutrients to enter.

In June, Szostak announced that his lab had constructed a model "protocell," a synthetic membrane enclosing a copy of an existing strand of genetic material. His team now is trying to synthesize the other half of the puzzle: some form of artificial DNA.

"We've made good progress on the cell membrane, leaving the genetic material as the major challenge," Szostak said.

George Church, a genetics professor at Harvard Medical School in Boston, and Anthony Forster, a pharmacologist at Vanderbilt University in Nashville, Tenn., are the co-authors of a plan to construct what they call a "minimal cell" containing only 151 genes. That's far fewer than the smallest natural microorganism, which has nearly 500.

The difficulties don't keep researchers from trying to simulate life, if not create it from a blank slate.

Steen Rasmussen, a physicist at the Los Alamos National Laboratory in New Mexico, heads a "Protocell Project." Its goal is to build lifelike artificial cells that are "self-reproducing and capable of evolution; self-containing, thereby possessing individual identity; self-sustaining in that they can maintain their complex structure."

Hundreds of scientists are working on less ambitious "synthetic biology" projects, aiming to develop useful products to cure diseases, clean up the environment and produce energy.

Church said that synthetic biologists didn't claim to be creating living organisms by "going from nothing to something." Instead, he said "nearly all such projects are inspired by existing molecules."

"What's new is our ability to construct more complex systems and evolve them in the lab, like going from abacus to laptop," he added.

A team led by Wimmer made a splash in 2002 when it synthesized the virus that causes polio. The feat set off a scare that terrorists might use his technique to make viruses for smallpox, Ebola or other deadly diseases.

Scientists don't consider a virus to be truly alive, because it has to take over a cell's DNA in order to reproduce. Instead, it occupies an intermediate state between living and nonliving.

"When it's outside the host cell, poliovirus is as dead as a pingpong ball," Wimmer said. "We did not create this virus," he said. "We merely reproduced poliovirus by following the blueprint of the viral genome."

There's a down side to synthetic biology. A recent report from the Center for Strategic and International Studies in Washington, a research center, cautioned that the ability to synthesize a virus in weeks may provide malefactors with "new ways to harm."

To reduce the risk, researchers weaken or omit key genes to prevent their artificial bugs from spreading.